MRAM is a non-volatile memory technology that stores data through magnetic storage elements. Because MRAM is non-volatile, memory written thereto may be retained even when the power supply of the MRAM is turned off. The magnetic storage elements used to actually store the data include two ferromagnetic plates, or electrodes, that can hold a magnetic field and are separated by a non-magnetic material, such as a non-magnetic metal or insulator. In general, one of the plates is referred to as the reference layer and has a magnetization which is pinned. In other words, the reference layer has a higher coercivity than the other plate and requires a larger magnetic field or spin-polarized current to change the orientation of its magnetization. The second plate is typically referred to as the free layer whose magnetization direction which can be changed by relatively smaller magnetic fields or a spin-polarized current relative to the reference layer.
MRAM devices store information by storing the orientation of the magnetization of the free layer. In particular, based on whether the free layer is in a parallel or anti-parallel alignment relative to the reference layer, either a logical “1” or a logical “0” can be stored in each respective MRAM cell. Due to the spin-polarized electron tunneling effect, the electrical resistance of a memory element changes due to the orientation of the magnetic fields of the two layers. The resistance of a cell will be different for the parallel and anti-parallel states and thus the cell's resistance can be used to distinguish between a logical “1” and a logical “0”.
An important and continuing goal in the data storage industry is that of increasing the density of data stored on a medium. For storage devices which implement MRAM, that goal has led to decreasing the footprint of individual MRAM cells in an attempt to further increase the storage capacity per unit area. However, the development of smaller MRAM cells has reached a limit which has effectively restricted conventional MRAM storage from further increasing storage density. Moreover, other types of random access memory are unable to achieve a storage density which rivals that of MRAM. For example, looking to FIGS. 1A-1B, a conventional transistor dynamic random access memory (DRAM) cell 100 is shown. Various components included in the DRAM cell are called out in FIGS. 1A-1B as would be appreciated by one skilled in the art.